It is common in the art to use lamp base shells to facilitate insertion and removal of a lamp into a corresponding lamp socket to establish electrical contact between the conductors of the lamp and the socket. Several structures have been developed to prevent the lamp base shell from being separated from the lamp base. See, for example, U.S. Pat. Nos. 1,262,936; 2,028,884; 2,157,051 and 5,006,751.
One method of securing a lamp base shell to a lamp utilizes a threaded inner shell having a washer-like base and a plurality of orthogonally projecting tabs around the periphery of the base to secure the lamp base shell to the lamp. The tabs of the inner shell each have a dimple that corresponds with an indentation in the neck of the lamp. The inner shell is secured to the lamp base by placing it over the neck until the corresponding dimples and indentations are aligned. Once the inner shell is in place, a lamp based shell is securely screwed onto the inner shell and is staked to engage it with the inner shell. This configuration requires expensive parts and involves difficult assembly.
Another method used to mechanically secure a base shell to a lamp employs a threaded form molded into the lamp glass with a keyway to accommodate a lead solder preform that is used to make an electrical connection to one of the lamp leads and to lock the base onto the lamp. Although this method provides sufficient back out torque resistance and addresses deficiencies of the inner shell technique, the use of lead solder has several disadvantages. Environmental laws and regulations continue to impose increasingly stringent standards that force the lamp industry to phase-out use of lead solder. Additionally, lead solder discolors the base shells of the lamps.
U.S. Pat. Nos. 5,381,070 (>070 patent) and 5,521,460 (>460 patent) disclose lamp base locking clips. The lamp base locking clip of the >070 patent includes a plate having a lip that extends outward on one end and has a flat portion on the opposite end. The locking clip is captured in a keyway formed on the glass neck of the lamp body. One of the lamp lead wires is welded to the flat portion of the clip and a rim on the lamp base shell is welded to the outwardly extending lip of the locking clip to form a lamp base assembly that does not include lead based solder.
The lamp base locking clip of the >460 patent has first and second ends of a given thickness and an intermediate portion that is at least approximately three times the thickness of the first and second ends. The lamp base locking clip is positioned in a keyway and connected to one lead in wire and the lamp base shell to secure the lamp base shell.